Plague Bats

This rune effect changes the damage type to poison, and causes the damage to scale up the longer a target is bathed in the rodent parade.

The tooltip for this skill is unclear. To clarify:
The total damage from this one slowly rises to 220%, however, the damage also has the additional effect of lingering on the target even while the Witch Doctor has finished casting.

A quick spray of Plague Bats will induce a small DoT effect, while an extended spray of Plague Bats will induce a more damaging, extended duration damage-over-time effect.